1. Field of the Invention
This invention relates to the molecular-weight reduction of nitrocellulose by means of electron beam radiation.
2. Description of the Prior Art
Nitrocellulose is a product of commerce which is available with variable nitrogen content in a wide range of viscosities. It is an excellent film-forming material useful in lacquers and other types of finishes, coating for cellophane, paper, fabrics and as a component of adhesives, etc. Heretofore nitrocellulose of reduced molecular weight has been prepared by a high temperature, acidic, hydrolytic process. One such process utilizes cellulose sheets in seven steps as follows:
1. comminute cellulose sheet, PA1 2. nitrate comminuted material, PA1 3. stabilize nitrated material in boiling water, PA1 4. digest slurry of nitrocellulose by passing through a digester coil at elevated temperature and pressure, PA1 5. wash, PA1 6. dehydrate material, and PA1 7. compress through rolls (densificated).
It is known from British Pat. No. 830,820 that controlled depolymerization of cellulose, especially in connection with the manufacture of viscose, can be accomplished by subjecting the cellulose to an absorbed dose of ionizing radiation between 0.05 and 60 watt-seconds/gram of cellulose (0.005 to 6.0 megarads). It is known that the stability of nitrocellulose is considerably less than that of cellulose. The nitrate group of nitrocellulose readily breaks down to form NO gas which combines with oxygen to form NO.sub.2. Not only could a fire develop from such breakdown, but the NO.sub.2 could combine with water or moisture to increase acidity and in turn increase degradation of the nitrocellulose. British Pat. No. 761,051 describes the subjecting of several polymers, including cellulose nitrate, to ionizing radiation in an amount sufficient to bring about an increase in the resistance of the substance to the solvent action of organic solvents but insufficient to cause any substantial change in the mechanical properties of the substance as measured at ordinary temperatures. The amount of ionizing radiation is a small quantity which crosslinks the cellulose nitrate increasing the molecular weight and thereby decreasing solubility. Polymer degradation is not disclosed. By irradiating nitrocellulose safely with relatively large absorbed dosages it has been found surprisingly that nitrocellulose of reduced molecular weight is prepared by a process which results in improved viscosity control, increased productivity and lower energy costs. The irradiation step replaces digestion step (4) described above.